If your computer isn’t 3D capable, you’ll still get Ubuntu Unity 3D renderings with your 2D graphic card. Starting with Ubuntu 12.10 (Quantal Quetzal), users who previously were assigned Unity 2D sessions in 12.04 because of unsupported graphic cards will automatically be transitioned to Unity 3D.
All features and benefits of 3D will be made available to you, thanks to this software driver. This is one more reason to switch to Unity.
Also, Unity 2D will no longer be available from Ubuntu’s Repository and will not be installable in Ubuntu 12.10.